With the development of direct liquefaction of coal, and since phenolic compounds are a product of this direct liquefaction, the supply of phenols present in tar acids will increase to the point where the tar acids will present a disposal problem. One possible solution is using these phenols as fuel extenders. Because of the toxicity and corrosiveness of phenols, however, they must be converted to less hazardous compounds for most fuel applications. Major alternatives to the disposal of these phenolic tar acids are hydrotreating and conversion to methyl aryl ethers. The claimed invention provides a method for converting these phenols to alkyl aryl ethers which are good octane boosters and anti-knock agents.
The model reaction for the formation of methyl aryl ethers is the formation of anisole from phenol and methanol.
U.S. Pat. No. 2,487,832 teaches a process for preparing anisole by the alkylation of phenols using dimethylether and a solid dehydrating catalyst. An example of such a solid dehydrating catalyst is alumina. Although alumina is a good catalyst for phenol alkylation, it has some selectivity for c-alkylation, producing cresols which are as toxic and corrosive as the phenols and therefore is not a suitable catalyst for phenol alkylation.
Another solid dehydrating catalyst, thoria, is also described in this patent. Thoria is highly selective for O-alkylation of phenol but its radioactivity makes it an unattractive alternative to other catalysts.
U.S. Pat. No. 3,642,912 also discloses a process for the catalytic alkylation of phenols. The catalysts described in this patent are titanium dioxide and derivatives thereof. These catalysts also prove to be good alkylating agents of phenols but, as with alumina, some selectivity to c-alkylation takes place producing unwanted cresols.
Anisole can also be selectively synthesized from sodium phenoxide and dimethylsulfate in the presence of NaOH. This process is known as the Williamson synthesis; see the Merck Index, Eighth Edition, 1968, page 1226. Because stoichiometric quantities of sodium hydroxide are required to produce the sodium phenoxide and because of the large quantities of salt by-product however, this type of process has little commercial appeal.